From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Prakash, Prashanth" Subject: Re: [PATCH v2] ACPI / Processor: add sysfs support for low power idle Date: Mon, 31 Jul 2017 12:18:08 -0600 Message-ID: <8beff6e7-e27c-0b44-6236-a95fcd5335d5@codeaurora.org> References: <1499968082-7753-1-git-send-email-pprakash@codeaurora.org> <3212e387-9f7d-5bd9-4612-79dddc77b05f@arm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Return-path: Received: from smtp.codeaurora.org ([198.145.29.96]:34638 "EHLO smtp.codeaurora.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751059AbdGaSSK (ORCPT ); Mon, 31 Jul 2017 14:18:10 -0400 In-Reply-To: <3212e387-9f7d-5bd9-4612-79dddc77b05f@arm.com> Content-Language: en-US Sender: linux-acpi-owner@vger.kernel.org List-Id: linux-acpi@vger.kernel.org To: Sudeep Holla , linux-acpi@vger.kernel.org Cc: rjw@rjwysocki.net, lenb@kernel.org, Lorenzo Pieralisi Hi Sudeep, On 7/31/2017 10:25 AM, Sudeep Holla wrote: > Sorry for the delay, I initial thought having this ABI under testing is > fine as I really don't want any *real* user space programs to depend on > this for various reasons stated in earlier threads, e.g. h/w auto > promotable states, accuracy of the stats, ..etc These fields are optional, so if there is no reliable way to keep track of stats, platform can choose not to expose it. If a platform is exposing inaccurate stats via this ACPI interface, it is breaking the spec. > But from Documentation/ABI/README, I see > > testing/ > This directory documents interfaces that are felt to be stable, > as the main development of this interface has been completed. > The interface can be changed to add new features, but the > current interface will not break by doing this, unless grave > errors or security problems are found in them. User space > programs can start to rely on these interfaces,... > > which makes me worry. Since the use for this is purely for debug or > optimization purposes, I still prefer simple single file debugfs entry. > I still can't digest the fact that reading single file is time consuming > as we are not using this interface at runtime IIUC. i.e. statistic are > collected and analyzed offline. These fields has the same utility/use-cases as the usage & time fields in cpuidle sysfs, but provides more granularity - idle stats for different levels hierarchy and accurate idle stats for states that require platform co-ordination. The argument for having a single sysfs file per node was that reading individual files might get expensive to get a snapshot(not the other way around). But, that argument was weak as we typically read these only in debug settings and not that often during runtime. So, the summary_stats file was removed and went with one value per file. -- Thanks, Prashanth